Pressure Pipes

ABSTRACT

A pressure pipe with increased long-term pressure resistance is comprised of a polypropylene composition. The polypropylene composition is comprised of a polyproyplene copolymer which is at least partially crystallised in the β-modification.

FIELD OF THE INVENTION

The invention relates to a pressure pipe with increased long-termpressure resistance which is comprised of a polypropylene composition.

BACKGROUND OF THE INVENTION

Polymer materials are frequently used for pipes for various purposes,such as fluid transport, i.e. transport of liquid or gas, e.g. water ornatural gas, during which the fluid can be pressurized. Moreover, thetransported fluid may have varying temperatures, usually within thetemperature range of about 0° C. to about 70° C. Such pipes arepreferably made of polyolefins, usually polyethylene or polypropylene.

Because of the high temperatures involved, hot water pipes of polymermaterials represent a particularly problematic type of polymer pipe. Notonly must a hot water polymer pipe fulfill the requirements necessaryfor other ordinary polymer pipes, such as cold water pipes, but inaddition it must withstand the strain associated with hot water. Thetemperatures of the hot water in a hot water pipe, typically used forplumbing and heating purposes, range from 30-70° C. which means that thepipe must be able to withstand a higher temperature than that for asecure long term use. Peak temperatures may be as high as 100° C.

According to the draft standard prEN 12202 a hot water polypropylenepipe must meet the requirement of at least 1000 h before failure at 95°C. and 3.5 MPa pressure if it is a random copolymer.

The Austrian patent AT 404 294 B discloses a pressure pipe whichconsists of a homopolymer of polypropylene which consists predominantlyof the hexagonal β-form of polypropylene with a nucleating agent whichis based on an amide. These pipes have an increased resistance to rapidcrack propagation.

The published Japanese patent application JP 05-170932 disclosespolypropylene pipes for watersupply purposes. It is disclosed, that byadding certain anti-oxidants to different kinds of polypropylene, theendurance time of these pipes can be increased.

None of these documents discloses polypropylene pipes with an increasedlong-term pressure resistance.

OBJECT OF THE INVENTION

It is therefore the object of the present invention to provide pressurepipes with an increased long-term pressure resistance which arecomprised of a polypropylene composition.

This object has been solved by a polypropylene composition which iscomprised of a propylene copolymer which comprises

-   -   73.0 -99.0 wt % of propylene and

1 to 20 wt % of one or more C₄-C₈ α-olefins and/or up to 7 wt % ofethylene, where the propylene copolymer is at least partiallycrystallized in the β-modification.

Long-term pressure resistance herein means a late occurrance of aknee-point when the pipe is tested according to ISO 1167:1996(E). Latemeans, that the occurance of a knee-point is shifted to a considerablyhigher failure time as for conventional polypropylene pipes. A lateoccurrance of a knee-point also usually encompasses that the slope of aregression line connecting the ductile failure points, in a log-logdiagram, is flatter than compared with present art.

Descriptions of ductile failure, brittle failure and knee-point (at agiven temperature): A ductile failure is defined as a macroscopicallyvisible deformation of the pipe geometry, e.g. a ruptured bubble. Abrittle failure or a weeping failure, which both are in the followingreferred to as non-ductile (n.d.), is defined as a failure which doesnot result in a visible deformation of the pipe geometry, e.g. cracks,fissures. A weeping failure typically has such a small crack, that itneeds to be visually inspected to see water penetrating out of the pipewall. Brittle failures are detected by pressure loss in the pipepressurising equipment. A knee-point at a given temperature is definedas the intersection of the regression line representing the ductilefailures and the regression line representing the non-ductile failures.

In order to calculate the lifetime of a pipe at longer times, pipes needto be pressure tested at different temperatures according to ISO 1167.Pressure test results at higher temperatures, e.g. at 110° C. or 95° C.,allow to extrapolate the life time of the pipe to lower temperatures.The extrapolation procedure is described in detail in the ISO TR 9080(1992) standard, commonly referred to as the standard extrapolatinmethod (SEM). This calculation method, which was defined for plasticspipes, fits a regression line in all the ductile breaks for a given testtemperature and a second regression line in the non-ductile breaks ofthis given temperature. The non-ductile lines are always steeper thanthe ductile lines. The calculation method is based on the combination ofthe set of failure data, where at a given temperature pipes are testedat different stress levels to get different failure times. Also pipeswhich are still “in progress”, i.e. no pipe failure has been observedand the time under test at a given time and stress is known, may also beadded to the set of data. This is particularly valid for pipes stillunder test at longer test times. Extrapolation time limits are alsodefined in this standard, e.g. when test results are available at 95° C.up to one year, these test results are allowed to be extrapolated to 55°C. (i.e. 95 minus 40) at 50 years. 50 years of extrapolation arerelevant for building pipes, but also shorter times such as 10 to 20years of extrapolation are relevant, e.g. for pipes for industrial use.The slopes of the lines of the non-ductile failures are steeper (i.e.more negative) than that of the ductile failures (when the samelog(failure time) vs. log(hoop stress) diagram is used as given in FIG.1). Since the point where the knee-point occurs, greatly influences theextrapolated stress at a given temperature, typically chosen between 30to 70° C., with extrapolated lifetimes from 10 to 50 years, it isdesireable for the knee-point to be at long times. The claim of theinvention is that the knee-point at a given temperature of the newproduct is shifted to longer times compared to present art.

It is also possible, when testing a pipe at a higher temperature such as95° C., that a knee-point is not observed within an investigation timeof 1 year, which is in fact a particularly preferred behaviour. In sucha case it is possible to use only ductile failures for extrapolation oflonger times.

The slope of the regression line of the ductile failure points has alarge influence on the extrapolated life times. It is thereforedesireable for this slope for a given temperature to be as large aspossible, i.e the regression line shall be as “flat” as possible(“large”, because in the display format of FIG. 1 the slopes arenegative values). It is part of the present invention, that theextrapolation line linking the ductile failure points for a giventemperature is flatter than present art.

It has surprisingly been found that pressure pipes which are comprisedof the above composition exhibit a remarkably improved behaviour wherelong-term pressure resistance is concerned.

The polypropylene composition of this invention is a composition of acopolymer of propylene with ethylene and/or an α-olefin.

This polypropylene copolymer is a copolymer which contains 73.0 to 99.0wt %, preferably 83.0-99.0 wt %, more preferably 85.5-97.0 wt % ofpropylene and 1 to 20 wt %, preferably 1.0-12.0 wt %, more preferably3.0-10.0 wt % of one or more C₄-C₈ α-olefins and/or up to 7.0 wt %,preferably up to 5.0 wt % and more preferably up to 4.5 wt % ofethylene.

The C₄-C₈ α-olefin is preferably selected from 1-butene, 1-pentene,1-hexene, 4-methyl-1-pentene and 1-octene. Particularly preferred is1-butene

The polymerisation process for the production of the polypropylenecopolymer may be a continuous process or a batch process, utilizingknown methods and operating in liquid phase, optionally in the presenceof an inert diluent, or in gas phase, or by mixed liquid-gas techniques.The process is preferably carried out in the presence of astereospecific Ziegler-Natta- or metallocene-catalyst system. Thecopolymer includes polypropylene copolymers with a monomodal as well aspolypropylene copolymers with a bimodal or multimodal molecular weightdistribution.

The “modality” of a polymer refers to the shape of its molecular weightdistribution curve, i.e. the appearance of the graph of the polymerweight fraction as function of its molecular weight. If the polymer isproduced in a sequential step process, utilizing reactors coupled inseries and using different conditions in each reactor, the differentfractions produced in the different reactors will each have their ownmolecular weight distribution. When the molecular weight distributioncurves from these fractions are superimposed into the molecular weightdistribution curve for the total resulting polymer product, that curvewill show two or more maxima or at least be distinctly broadened incomparison with the curves for the individual fractions. The molecularweight distribution of such a polymer product, produced in two or moreserial steps, is called bimodal or multimodal, depending on the numberof steps.

According to a further embodiment the pipe is comprised of a propylenecopolymer which is comprised of

-   -   83.0-99.0 wt % of propylene and    -   1 to 12 wt % of one or more C₄-C₈ α-olefins and/or up to 5.0 wt        % of ethylene.

Pipes from these polypropylene compositions exhibit still betterlong-term pressure resistances.

According to the present invention the polypropylene composition has anMFR of 0.1 to 10 g/10 min at 230° C./2.16 kg. Preferred MFR values 0.1to 5, more preferably 0.1 to 2, and most preferably MFR values below 1g/10 min at 230° C./2.16 kg.

According to a still further embodiment of the present invention thepropylene copolymer is a random polymer.

It is advantageous for the pipes according to the invention when theamount of β-crystallinity of the polypropylene copolymer (determined byDSC using the second heat) is at least 50%, preferably at least 60%,more preferably at least 70% and most preferably at least 80%.

According to an advantageous embodiment the propylene copolymercomprises a β-nucleating agent, of which any one or mixtures of a mixedcrystal of 5,12-dihydro-quino(2,3-b)acridine-7,14-dione withquino(2,3-b)acridine-6,7,13,1 4(5H, 1 2H)-tetrone,N,N′-dicyclohexyl-2,6-naphtalen dicarboxamide and salts of dicarboxylicacids with at least 7 carbon atoms with metals of group 11 of theperiodic table are preferred.

A preferred composition is comprised of a propylene copolymer which iscomprised of 89.0-96.0 wt % of propylene and

-   -   3 to 10 wt % of butene and up to    -   1.0 wt % of ethylene.

It is a further object of the present invention to provide a novel wayof producing polypropylene pressure pipes with a reduced sensitivity ofthe measured failure times to the applied hoop stress.

The above object is achieved by using a polypropylene compositioncomprised of a propylene copolymer which comprises

-   -   73.0-99.0 wt % of propylene and    -   1 to 20 wt % of one or more C₄-C₈ α-olefins and/or up to 7 wt %        of ethylene, where the propylene copolymer is at least partially        crystallized in the β-modification, for the production of        pressure pipes whose failure time vs. hoop stress relation at        95° C. before a knee-point fits the following type of equation:        LOG (hoop stress)=(slope)*LOG(failure time)+(constant),        where (slope)≧−0.0300 when the failure is ductile and where the        testing is performed according to ISO 1167:1996(E).

All known polypropylene pipes which are state of the art exhibit aremarkably steeper slope, i.e. more negative (slope)-values, in theregion of ductile failure when they are tested according to the aboveconditions.

In the above equation the item (constant) is dependent upon the chemicalcomposition of the tested polymer, e.g. whether it is a homo- orcopolymer. The value of (constant) alone does not give any indicationabout the pressure resistance properties of a pipe.

It is a still further object of the present invention to providepolypropylene pressure pipes with an increased long-term pressureresistance, i.e. a delayed occurrence of a knee-point in their failuretime vs. hoop stress relation.

The above object is solved by using a polypropylene compositioncomprised of a propylene copolymer which comprises

-   -   73.0-99.0 wt % of propylene and    -   1 to 20 wt % of one or more C₄-C₈ α-olefins and/or up to 7 wt %        of ethylene, where the propylene copolymer is at least partially        crystallized in the β-modification, for the production of        pressure pipes whose failure time vs. hoop stress relation at        95° C. before a knee-point fits the following type of equation:        LOG(hoop stress)=(slope)*LOG(failure time)+(constant)        and where a knee-point does not occur before 1500 hrs of testing        according to ISO 1167:1996(E).

All known polypropylene random copolymer pipes which are state of theart have a knee-point of no longer than 1500 hrs, when pressure testingat 95° C. according to ISO 1167:1996(E). At the date of filing thisapplication (November 2001) only ductile failures and no non-ductilefailures have been observed at 95° C. and 70° C. with pipes according tothe invention, with some pipes having already been tested for more than10.000 hrs. Consequently, no knee-point has been observed.

According to an embodiment of the present invention the propylenecopolymer comprises

-   -   90.0-94.0 wt % of propylene and    -   6 to 10 wt % of 1-butene,        where (slope)≧−0.0250.

Pressure pipes from the above compositions of propylene/1-butenecopolymers have a very flat slope in their ductile failure region.

According to a further embodiment of the present invention the propylenecopolymer comprises

-   -   89.4-95.9 wt % of propylene and    -   4 to 10 wt % of 1-butene and    -   0.1 to 0.6 wt % of ethylene,        where (slope)≧″0.0250.

Pressure pipes from compositions comprising terpolymers of propylene,1-butene and small amounts of ethylene also have very favourable flatslopes in their ductile failure region.

According to a still further embodiment of the present invention thepropylene copolymer comprises

-   -   95-97 wt % of propylene and    -   3 to 5 wt % of ethylene        where (slope)≧−0.0220.

Pressure pipes from the above compostions comprising propylene/ethylenecopolymers also have very favourable flat slopes in their ductilefailure region.

Definition of β-Nucleating Agent

As β-nucleating agent any nucleating agent can be used which is suitablefor inducing crystallization of polypropylene homo- and copolymers inthe hexagonal or pseudohexagonal modification. Mixtures of suchnucleating agents may also be employed.

Suitable types of 13-nucleating agents are

-   -   dicarboxylic acid derivative type diamide compounds from        C₅-C₈-cycloalkyl monoamines or C₆-C₁₂-aromatic monoamines and        C₅-C₈-aliphatic, C₅-C₈-cycloaliphatic or C₆-C₁₂-aromatic        dicarboxylic acids, e.g.        -   N,N′-di-C₅-C₈-cycloalkyl-2,6-naphthalene dicarboxamide            compounds such as N,N′-dicyclohexyl-2,6-naphthalene            dicarboxamide and N,N′-dicyclooctyl-2,6-naphthalene            dicarboxamide,        -   N,N′-di-C₅-C₈-cycloalkyl-4,4-biphenyidicarboxamide compounds            such as N,N′-dicyclohexyl-4,4-biphenyidicarboxamide and            N,N′-dicyclopentyl-4,4-biphenyldicarboxamide,        -   N,N′-di-C₅-C₈-cycloalkyl-terephthalamide compounds such as            N,N′-dicyclohexylterephthalamide and            N,N′-dicyclopentylterephthalamide,        -   N,N′-di-C₅-C₈-cycloalkyl-1,4-cyclohexanedicarboxamide            compounds such as            N,N′-dicyclo-hexyl-1,4-cyclohexanedicarboxamide and            N,N′-dicyclohexyl-1,4-cyclopentanedicarboxamide,    -   diamine derivative type diamide compounds from C₅-C₈-cycloalkyl        monocarboxylic acids or C₆-C₁₂-aromatic monocarboxylic acids and        C₅-C₈-cycloaliphatic or C₆-C₁₂-aromatic diamines, e.g.        -   N,N′-C₆-C₁₂-arylene-bis-benzamide compounds such as            N,N′-p-phenylene-bis-benzamide and            N,N′-1,5-naphthalene-bis-benzamide,        -   N,N′-C₅-C₈-cycloalkyl-bis-benzamide compounds such as            N,N′-1,4-cyclopentane-bis-benzamide and            N,N′-1,4-cyclohexane-bis-benzamide,        -   N,N′-p-C₆-C₁₂-arylene-bis-C₅-C₈-cycloalkylcarboxamide            compounds such as            N,N′-1,5-naphthalene-bis-cyclohexanecarboxamide and            N,N′-1,4-phenylene-bis-cyclohexanecarboxamide, and        -   N,N′-C₅-C₈-cycloalkyl-bis-cyclohexanecarboxamide compounds            such as N,N′-1,4-cyclopentane-bis-cyclohexanecarboxamide and            N,N′-1,4-cyclohexane-bis-cyclohexanecarboxamide,    -   amino acid derivative type diamide compounds from amidation        reaction of C₅-C₈-alkyl, C₅-C₈-cycloalkyl- or C₆-C₁₂-arylamino        acids, C₅-C₈-alkyl-, C₅-C₈-cycloalkyl- or C₆-C₁₂-aromatic        monocarboxylic acid chlorides and C₅-C₈-alkyl-,        C₅-C₈-cycloalkyl- or C₆-C₁₂-aromatic mono-amines, e.g.        -   N-phenyl-5-(N-benzoylamino)pentaneamide and            N-cyclohexyl-4-(N-cyclohexyl-carbonylamino)benzamide.

Further suitable β-nucleating agents are

-   -   quinacridone type compounds, e.g. quinacridone,        dimethylquinacridone and dimethoxyquinacridone,    -   quinacridonequinone type compounds, e.g. quinacridonequinone, a        mixed crystal of 5,12-dihydro(2,3b)acridine-7,14-dione with        quino(2,3b)acridine-6,7,13,1 4-(5H,1 2H)-tetrone and        dimethoxyquinacridonequinone and    -   dihydroquinacridone type compounds, e.g. dihydroquinacridone,        dimethoxydihydroquinacridone and dibenzodihydroquinacridone.

Still further suitable β-nucleating agents are

-   -   dicarboxylic acid salts of metals from group IIa of periodic        system, e.g. pimelic acid calcium salt and suberic acid calcium        salt; and    -   mixtures of dicarboxylic acids and salts of metals from group        IIa of periodic system.

Still further suitable β-nucleating agents are

-   -   salts of metals from group IIa of periodic system and imido        acids of the formula        wherein x=1 to 4; R═H, —COOH, C₁-C₁₂-alkyl, C₅-C₈-cycloalkyl or        C₆-C₁₂-aryl, and Y =C₁-C₁₂-alkyl, C₅-C₈-cycloalkyl or        C6-C₁₂-aryl-substituted bivalent C₆-C₁₂-aromatic residues, e.g.    -   calcium salts of phthaloylglycine, hexahydrophthaloylglycine,        N-phthaloylalanine and/or N4-methylphthaloylglycine.

Preferred β-nucleating agents are any one or mixtures ofN,N′-dicyclohexyl-2,6-naphtalene dicarboxamide, the β-nucleating agentsof EP 170889 and those of EP 682066.

The propylene copolymer which is at least partly crystallized in theβ-modification is preferably produced by melt mixing the propylenecopolymer base resin with 0.0001 to 2.0 wt % based on the propylenecopolymer used, of 1-nucleating agents at temperatures from 175 to 250°C. and cooling and crystallizing the melt according to procedures whichare state of the art.

Definition of Pipe

The term “pipe” as used herein is meant to encompass pipes in thenarrower sense, as well as supplementary parts like fittings, valves andall parts which are commonly necessary for e.g. a hot water pipingsystem.

Pipes according to the invention also encompass single and multilayerpipes, where for example one or more of the layers is a metal layer andwhich may include an adhesive layer. Other constructions of pipes, e.g.corrugated pipes, are possible as well.

The propylene compositions used for pipes according to the invention maycontain usual auxiliary materials, e.g. up to 40 wt % fillers and/or0.01 to 2.5 wt % stabilizers and/or 0.01 to 1 wt % processing aidsand/or 0.1 to 1 wt % antistatic agents and/or 0.2 to 3 wt % pigmentsand/or reinforcing agents, e.g. glass fibres, in each case based on thepropylene composition used.

For the present invention coloration of the propylene composition islargely irrelevant, however certain pigments, e.g. pigments which arehighly active a-nucleating agents, cannot be utilised.

Production of the Pipes

Pipes according to the invention were produced by first plasticizing thepropylene polymer in an extruder at temperatures in the range of from200 to 250° C. and then extruding it through an annular die and coolingit.

The extruders for producing the pipes can be single screw extruders withan LID of 20 to 40 or twin screw extruders or extruder cascades ofhomogenizing extruders (single screw or twin screw). Optionally, a meltpump and/or a static mixer can be used additionally between the extruderand the ring die head. Ring shaped dies with diameters ranging fromapproximately 16 to 2000 mm and even grater are possible.

The melt arriving from the extruder is first distributed over an annularcross-section via conically arranged holes and then fed to the core/diecombination via a coil distributor or screen. If necessary, restrictorrings or other structural elements for ensuring uniform melt flow mayadditionally be installed before the die outlet.

After leaving the annular die, the pipe is taken off over a calibratingmandrel, usually accompanied by cooling of the pipe by air coolingand/or water cooling, optionally also with inner water cooling.

Experimental Part—Preparation of the Polymer Compositions

Base Resin I

The Propene-1-butene-copolymer was polymerized in a continuous workingpolymerization system by using propene, 1-butene, the catalyst compoundC and cocatalysts (Triethylaluminium (TEAI), Electron donor (CMDMS)).

Catalyst Compound C

As catalyst compound C a commercial available Ziegler/Natta-catalyst(Titaniumchloride catalyst supported on MgCl₂), suitable for theproduction of polypropylene-copolymers in a monomer suspension is used.

Polymerization

The polymerization is performed continuously in a prepolymerizationreactor and a main polymerization reactor. Temperatures, pressures,catalyst-, monomer- and hydrogen feed in the separate polymerizationsteps as well as the polymer concentration in the main reactor are keptconstant. The molar mass of the copolymer is controlled by addinghydrogen gas. The concentration of hydrogen in the mixture of liquidmonomers is continuously measured by gas chromatography. The relevantprocessing parameters and the analytical results of the resultingpolymer are listed in table 1.

The first polymerization step is performed in a small reactor (equippedwith stirrer and cooling system), where an excess of a liquid mixture ofthe monomers propene and 1-butene is prepolymerized for 9 minutes at 20°C. Therefore catalyst compound C, mixed with the cocatalyst compoundsTriethylaluminium (TEAI) and Cyclohexyl-methyl-dimethoxysilane (CMDMS)as external electron donor, are continuously poured into theprepolymerization unit.

The prepolymer (product A) is continuously removed from theprepolymerization unit and passed over into the main reactor system(equipped with stirrer and cooling system), where under excess of aliquid mixture of the monomers propene and 1-butene, the final copolymer(B) is formed. Further a mixture of monomers (propene/1-butene) andhydrogen (for molar mass control) are continuously fed into the mainreactor. The polymer concentration is kept constant at 517 g/l. A partof the reactor content (polymer-/monomer excess) is continuously removedfrom the reactor into a degassing unit to separate the formed copolymer(B) from unreacted monomer mixture by evaporation.

The separated copolymer (B), Base resin I was subjected to a steamtreatment, to remove the unreacted monomers and volatile substances, andthen dried.

Base Resin II

The Propene-1-butene-copolymer was polymerized in a continuous workingpolymerization system by using propene, 1-butene, the catalyst compoundF and cocatalysts (Triethylaluminium (TEAI), Electron donor (DCPDMS)).

Catalyst Compound F

As catalyst compound F a commercial available Ziegler/Natta-catalyst(Titaniumchloride catalyst supported on MgCl₂), suitable for theproduction of polypropylene-copolymers in a monomer suspension is used.

Polymerization

The polymerization is performed continuously in a prepolymerizationreactor and a main polymerization reactor. Temperatures, pressures,catalyst-, monomer- and hydrogen feed in the separate polymerizationsteps as well as the polymer concentration in the main reactor are keptconstant. The molar mass of the copolymer is controlled by addinghydrogen gas. The concentration of hydrogen in the mixture of liquidmonomers is continuously measured by gas chromatography. The relevantprocessing parameters and the analytical results of the resultingpolymer are listed in table 1.

The first polymerization step is performed in a small reactor (equippedwith stirrer and cooling system), where an excess of propene and1-butene is prepolymerized for 9 minutes at 20° C. Catalyst compound F,mixed with the cocatalyst compounds Triethylaluminium (TEAI) andDicyclopentyl-dimethoxysilan (DCPDMS) as external electron donor, arecontinuously poured into the prepolymerization unit.

The prepolymer (product D) is continuously removed from theprepolymerization unit and passed over into the main reactor system(equipped with stirrer and cooling system), where under excess of aliquid mixture of the monomers propene and 1-butene, the final copolymer(E) is formed. Further a mixture of monomers (propene/ethene) andhydrogen (for molar mass control) are continuously fed into the mainreactor. The polymer concentration is kept constant at 513 g/l. A partof the reactor content (polymer-/monomer excess) is continuously removedfrom the reactor into a degassing unit to separate the formed copolymer(E) from unreacted monomer mixture by evaporation.

The separated copolymer (E), Base resin II was subjected to a steamtreatment, to remove the unreacted monomers and volatile substances, andthen dried

Base Resin III

The Propene-ethene-1-butene-terpolymer was polymerized in a continuousworking polymerization system by using propene, ethene, 1-butene, thecatalyst compound J and cocatalysts (Triethylaluminium (TEAI), Electrondonor (CMDMS)).

Catalyst Compound J

As catalyst compound J a commercial available Ziegler/Natta-catalyst(Titaniumchloride catalyst supported on MgCl₂), suitable for theproduction of polypropylene terpolymers in a monomer suspension is used.

Polymerization

The polymerization is performed continuously in a prepolymerizationreactor and a main polymerization reactor. Temperatures, pressures,catalyst-, monomer- and hydrogen feed in the separate polymerizationsteps as well as the polymer concentration in the main reactor are keptconstant. The molar mass of the terpolymer is controlled by addinghydrogen gas. The concentration of hydrogen in the mixture of liquidmonomers is continuously measured by gas chromatography. The relevantprocessing parameters and the analytical results of the resultingpolymer are listed in tables 1 and 2.

The first polymerization step is performed in a small reactor (equippedwith stirrer and cooling system), where an excess of a liquid mixture ofthe monomers propene and 1-butene is prepolymerized for 9 minutes at 20°C. Therefore catalyst compound J mixed with the cocatalyst compoundsTriethylaluminium (TEAI) and Cyclohexyl-methyl-dimethoxysilane (CMDMS)as external electron donor, are continuously poured into theprepolymerization unit.

The prepolymer (product K) is continuously removed from theprepolymerization unit and passed over into the main reactor system(equipped with stirrer and cooling system), where under excess of aliquid mixture of the monomers propene and 1-butene, under addition ofethene, the final terpolymer (L) is formed. Further a mixture ofmonomers (propene/1-butene/ethene) and hydrogen (for molar mass control)are continuously fed into the main reactor. The polymer concentration iskept constant at 542 g/l. A part of the reactor content(polymer-/monomer excess) continuously is removed from the reactor intoa degassing unit to separate the formed terpolymer (L) from unreactedmonomer mixture by evaporation.

The separated terpolymer (L), Base resin III, was subjected to a steamtreatment, to remove the unreacted monomers and volatile substances, andthen dried. TABLE 1 Base resins Parameter unit I II III Catalyst systemand concentration TEAL/CMDMS g/g 4.85 — 4.85 TEAI/DCPDMS g/g — 4.85 —TEAI/Ti g/g 218 315 317 TEAI/Ti mol/mol 91 132 133 Prepolymerizationreactor/Liquid monomer phase Catalyst compound — C F J Feed catalystcompound g/h 4.04 2.78 3.18 Pressure bar 34 34 34 Temperature ° C. 20 2020 mean residence time min 9 9 9 Main reactor/Liquid monomer phasePressure bar 34 34 34 Temperature ° C. 65 65 65 Average residence timecatalyst min 1.48 1.46 1.50 Polymer concentration in reactor g/l 517 513542 (stationary) Feed propylen/1-butene mixture kg/h 130 130 134 Butenecontent in monomer feed Vol % 12.5 13.0 22.0 Ethylene feed kg/h — — 0.8H2-concentration based on ppm 95 210 110 monomer feed Polymer productionrate final kg/h 41.0 30.0 49.5 product Final product — B E K Analyticalresults MFR (230°/2.16 kp) g/10 min 0.27 0.41 0.32 Ethylene content incopolymer wt % 0 0 0.6 Butene content in copolymer wt % 6.2 6.6 6.1Xylene cold solubles wt-% 3.8 2.7 4.1 Melting temperature ° C. 145 142142

EXAMPLE 1 (INVENTION)

The Propene-1-butene-copolymer powder (Base resin I) was mixed with0.07% Calciumstearate, 0.25%Pentaerythritol-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,0.1% Tris(2,4-ditert-butylphenyl)phosphite, 0.25%3,3′,3′,5,5′,5′-hexa-tert-butyl-a,a′,a′-(mesitylene-2,4,6-triyl)tri-p-cresoland 2% Masterbatch A and pelletized in a conventional compounding line.

EXAMPLE 2 (INVENTION)

The Propene-1-butene-copolymer powder (Base resin II) was mixed with0.07% Calciumstearate, 0.25%Pentaerythritol-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,0.1% Tris(2,4-ditert-butylphenyl)phosphite, 0.25%3,3′,3′,5,5′,5′-hexa-tert-butyl-a,a′,a′-(mesitylene-2,4,6-triyl)tri-p-cresoland 2% Masterbatch A and pelletized in a conventional compounding line.

EXAMPLE 3 (INVENTION)

The Propene-ethene-1-butene-terpolymer powder (Base resin III) was mixedwith 0.07% Calciumstearate, 0.25%Pentaerythritol-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,0.1% Tris(2,4-ditert-butylphenyl)phosphite, 0.25%3,3′,3′,5,5′,5′-hexa-tert-butyl-a,a′,a′-(mesitylene-2,4,6-triyl)tri-p-cresoland 2% Masterbatch A and pelletized in a conventional compounding line.

EXAMPLE 4 (INVENTION)

The Propene-ethene-1-butene-terpolymer powder (Base resin III) was mixedwith 0.07% Calciumstearate, 0.25%Pentaerythritol-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,0.1% Tris(2,4-ditert-butylphenyl)phosphite, 0.25%3,3′,3′,5,5′,5′-hexa-tert-butyl-a,a′,a′-(mesitylene-2,4,6-triyl)tri-p-cresoland 0.1% Calciumpimelate and pelletized in a conventional compoundingline.

EXAMPLE 5 (INVENTION)

The commercially available Propene-ethene-copolymer Borealis RA130E wasmixed with 0.5% Dioctadecyl 3,3′-thiodipropionate and 2% Masterbatch Aand pelletized in a conventional compounding line.

COMPARATIVE EXAMPLE 1

The Propene-1-butene-copolymer powder (Base resin I) was mixed with0.07% Calciumstearate, 0.25%Pentaerythritol-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,0.1% Tris(2,4-ditert-butylphenyl)phosphite, 0.25%3,3′,3′,5,5′,5′-hexa-tert-butyl-a,a′,a′-(mesitylene-2,4,6-triyl)tri-p-cresoland pelletized in a conventional compounding line.

COMPARATIVE EXAMPLE 2

The Propene-1-butene-copolymer powder (Base resin II) was mixed with0.07% Calciumstearate, 0.25%Pentaerythritol-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,0.1% Tris(2,4-ditert-butylphenyl)phosphite, 0.25%3,3′,3′,5,5′,5′-hexa-tert-butyl-a,a′,a′-(mesitylene-2,4,6-triyl)tri-p-cresoland pelletized in a conventional compounding line.

COMPARATIVE EXAMPLE 3

The Propene-ethene-1-butene-terpolymer powder (Base resin III) was mixedwith 0.07% Calciumstearate, 0.25%Pentaerythritol-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,0.1% Tris(2,4-ditert-butylphenyl)phosphite, 0.25%3,3′,3′,5,5′,5′-hexa-tert-butyl-a,a′,a′-(mesitylene-2,4,6-triyl)tri-p-cresoland pelletized in a conventional compounding line.

COMPARATIVE EXAMPLE 4

As comparative example 4 a commercially availablepropene-ethene-copolymer grade (Borealis RA 130E) was used.

COMPARATIVE EXAMPLE 5

As comparative example 5 a commercial available propene-homopolymergrade (Borealis BE60-7032) was used.

Masterbatch A

Masterbatch A is a commercially available product based on polypropyleneand containing the quinacridone pigment “Chinquasia gold” asβ-nucleating agent. Composition of Masterbatch A: 49.75% Polypropylene 0.25% Quinacridone Pigment Orange 48    2% Carbon Black Pigment Black 7   4% Cr/Sb/Ti oxide Pigment Brown 24    1% Chromium oxide Pigment Green17    1% Ni/Sb/Ti oxide Pigment Yellow 53   42% TiO₂ Pigment White 6Calciumpimelate

1 Mol of pimelic acid was reacted with 1 mol calciumcarbonate in amixture of ethanol and water at 60-80° C. The produced calciumpimelatewas filtered and dried.

Description of Measurement Methods

Determination of β-Crystallinity

The β-crystallinity was determined by Differential Scanning Calorimetry(DSC). DSC was run according to ISO 3146/part 3/method C2 with a scanrate of 10° C./min. The amount of 13-modification was calculated fromthe second heat by the following formula:β-area/(α-area+βp-area)

Since the thermodynamical instable β-modification starts to be changedinto the more stable a-modification at temperatures above 150° C., apart of the β-modification is transferred within the heating process ofDSC-measurement. Therefore the amount of β-PP determined by DSC is loweras when measured according to the method of Turner-Jones by WAXS (A.Turner-Jones et. al., Makromol. Chem 75 (1964) 134).

“Second heat” means, that the sample is heated according to ISO3146/part 3/method C2 for a first time and then cooled to roomtemperature at a rate of 20° C./min. The sample is then heated a secondtime, also according to ISO 3146/part 3/method C2. This second heat isrelevant for measurement and calculation.

During the “first heat” all thermal history of the sample giving rise todifferent crystalline structure, which typically comes from differentprocessing conditions and/or methods, is destroyed. Using the secondheat for determination of β-crystallinity, it is possible to comparesamples regardless of the way the samples were originally manufactured.

XCS

Xylene solubles were determined at 23° C. according to ISO 6427. Xylenesolubles are defined as the percent by weight that stays in solutionafter the polymer sample is dissolved in hot xylene and the solution isallowed to cool to 23° C.

MFR

The melt flow rates were measured with a load of 2.16 kg at 230° C. Themelt flow rate is that quantity of polymer in grams which the testapparatus standardized to DIN 53 735 extrudes within 10 minutes at atemperature of 230° C. under a weight of 2.16 kg.

Flexural Test

The flexural test was carried out according to the method of ISO 178 byusing injection molded test specimens as described in EN ISO 1873-2(80×10×4 mm).

Charpy Impact Strength

The notched charpy impact strength was carried out according to ISO179/1 eA at 23° C. by using injection molded test specimens as describedin EN ISO 1873-2 (80×10×4 mm)

Hoop Stress Test

Hoop stress tests are performed according to ISO 1167:1996(E). For abetter comparability and also for practical reasons (availability ofdata) only the data at 95° C. are used in this application. TABLE 2 Dataof basic polymer Base resin BE60 RA130E Base resin I Base resin II Baseresin III Example CE 5 CE 4 E 5 CE 1 E 1 CE 2 E 2 CE 3 E 3 E 4 CommentC2-raco C4-raco C4-raco C2C3C4-raco Nucleation β α β α β α β α β ββ-nucleating agent Masterbatch A ppm 12000 12000 20000 20000 20000Calciumpimelate ppm 1000 Analytical & mechanical results MFR 230/2.16g/10′ 0.3 0.19 0.20 0.21 0.25 0.31 0.35 0.33 0.35 0.35 DSC Tm ° C. 152143 132 143 135 143 134 140 131 133 168 146 149 148 144 145 Hm J/g 90 8162 80 67 92 69 78 63 66 21 16 12 12 12 15 Tc ° C. 124 103 109 102 108 98106 99 104 105 β- (DSC) % 81 80 84 85 84 81 nucleation IR ethylene wt %4.2 4.2 0.6 0.6 0.6 1-butene wt % 8.3 8.3 8.6 8.6 8.2 8.2 8.2 ExtractionXCS % 2.3 6.9 7.5 3.1 2.1 2.2 2.8 3.2 3.4 2.9 Iso 179 +23° C. kJ/m² 8518 90 12 82 9 74 11 84 76 notched Flex test Flex Mod MPa 1215 828 740972 959 1051 998 949 902 888 Failure times [h]/Failure mode hoop 3.5 MPa7845/nD 7663/nD 6298/D 13000 ip 13000 ip 4323/nD 13000 ip 12000 ip 12000ip 12000 ip stress at 3.8 MPa 6946/nD 3020/nD  59/D 7185/nD 5885/D10558/D 6712/nD 5269/D 5317/D 95° C. 4.0 MPa 6511/nD 2264/nD   7/D 248/D  1301/D  199/D  204/D 4.2 MPa 1079/nD 2855/nD  49/D 2860/nD  71/D 2499/nD  37/D  36/D 4.5 MPa 2769/nD  684/nD 1151/nD   6/D  866/nD  8/D 1022/nD   6/D   5/D 4.9 MPa 220/D 5.0 MPa 1939/nD 120/D 5.1 MPa 80/D 5.2 MPa  44/D 5.5 MPa 726/D 6.0 MPa  58/DFailure modes:D . . . ductile failurenD . . . non-ductile failureip . . . testing in progress, no failure until specified time.

Comparative examples CE4 and CE5 show both ductile and non-ductilefailures at 95° C. A regression line through the non-ductile failurepoints, when put into a log/log diagram as explained earlier, is steeperthan one through the ductile failure points (for each example), when putinto a log/log diagram. Therefore all of the comparative examples CE4and CE5 display a knee-point. On the other hand, examples El-E4according to the invention do not show any non-ductile failure points,all failure points, including the “ip—in progress” pipes lay on astraight line. Testing is under way for more than one year (i.e. 12000and 13000 hours) and only ductile failure points can be used ofextrapolation in order to get the extrapolated life time at 50° C.

The longest knee-points at 95° C. for present art are at the followingtimes: CE1<1151 h (nD); CE2≦866 h (nD); CE3≦1022 h (nD); CE4: between220 h (D) and 684 h (nD); CE5: between 726 h (D) and 1939 h (nD).

The examples according to the invention (E1 to E4) do not showknee-points at times >5885 h (D) for E1; >10558 h (D) for E2; >5269 h(D) for E3 and >5217 h (D) for E4 and at times of >12000 h and >13000 hall pipes are still in progress. Only one straight line is present forEl to E4, thus higher stress levels will be achieved when extrapolatedto lower temperatures to 10 to 50 years.

Comparing the slopes of CE1 to CE5 it is evident that they are steeperthan the slopes of E1 to E4 in their ductile region.

E3 and E4, two beta-nucleated ethene-propene-butene terpolymers, show,when compared to CE3, a non beta-nucleated terpolymer of the same baseresin, that the same phenomena like much prolonged or non-presentknee-point and flatter ductile line also hold for ethene-propene-buteneterpolymers.

E1 and E2, two beta-nucleated propene-butene copolymers, show, whencompared to CE1 and CE2, non beta-nucleated propene-butene copolymers ofthe same base resin, that the same phenomena like much prolonged ornon-present knee-point and flatter ductile line also hold forpropene-butene copolymers.

E5, a beta-nucleated ethene-propene copolymer, show, when compared toCE4, a non beta-nucleated ethene-propene copolymer of the same baseresin, that the same phenomena like much prolonged or non-presentknee-point and flatter ductile line also hold for ethene-propenecopolymers.

The diagram in FIG. 1 is a log/log representation of comparativeexamples CE4 and CE5 and of inventive example E2. The lines which aredrawn through the data points of CE4 and CE5 are drawn by hand. It ishowever clearly visible, that for each set of data—with the exception ofE2—a distinctive knee-point is present at the intersection of therespective ductile and non-ductile regression lines. It is also clearlyvisible that the slopes of the regression lines of CE4 and CE5 in theirductile region is steeper than the slope of the regression line of E2.The number of data points in the non-ductile region of CE4 and CE5 isdifferent from the number of data presented in table 2. This doeshowever not change the time of occurrence of a knee-point or the slopeof the regression line in the ductile region.

The regression line through the data points of ductile failure of E2 isexactly calculated and the equation of the regression line (which isactually a polynomial regression curve, which appears as a straight linein the double logarithmic representation) is included in FIG. 1. Theexponent in the equation is what is referred to herein as (slope).

The single data point which is denoted as E2 (i.p.), which means thatthe pipe is still under testing, is not included in the regressionanalysis. This data point will slowly continue to move to the right ofthe diagram as time progresses and it will either be the firstnon-ductile failure point of this data series (after more than 13000hours !) or a still further ductile failure point.

1. Pressure pipe with increased long-term pressure resistance comprisedof a polypropylene composition wherein the polypropylene composition iscomprised of a propylene random copolymer which comprises 73.0-99.0 wt %of propylene, and 1 to 20 wt % of one or more C₄-C₈ α-olefins and/or upto 7.0 wt % of ethylene, where the propylene random copolymer is atleast partially crystallized in the β-modification.
 2. Pipe according toclaim 1, wherein the propylene random copolymer is comprised of:83.0-99.0 wt % of propylene, and 1 to 12 wt % of one or more C₄-C₈α-olefins and/or up to 5.0 wt % of ethylene.
 3. Pipe according to anyone of claims 1 or 2 wherein the polypropylene composition has an MFR of0.1 to 10 g/10 min at 230° C./2.16 kg.
 4. (Cancel)
 5. Pipe according toany one of claims 1 or 2 wherein the amount of β-crystallinity of thepolypropylene random copolymer determined by DSC using the second heatis at least 50%.
 6. Pipe according to any one of claims 1 or 2 whereinthe propylene random copolymer comprises a β-nucleating agent.
 7. Pipeaccording to claim 6 wherein the β-nucleating agent comprises any one ormixtures of a mixed crystal of5,12-dihydro-quino(2,3-b)acridine-7,14-dione withquino(2,3-b)acridine-6,7,13,14(5H, 12H)-tetrone,N,N′-dicyclohexyl-2,6-naphtalen dicarboxamide and salts of dicarboxylicacids with at least 7 carbon atoms with metals of group II of theperiodic table.
 8. Pipe according to any one of claims 1 or 2 whereinthe propylene random copolymer is comprised of: 89.0-96.0 wt % ofpropylene, 3 to 10 wt % of butene, and up to 1.0 wt % of ethylene. 9.Use of a A polypropylene composition comprised of a propylene randomcopolymer which comprises: 73.0-99.0 wt % of propylene, and 1 to 20 wt %of one or more C₄-C₈ α-olefins and/or up to 7 wt % of ethylene, wherethe propylene random copolymer is at least partially crystallized in theβ-modification, for the production of pressure pipes whose failure timevs. hoop stress relation at 95° C. before a knee-point fits thefollowing type of equation:LOG(hoop stress)=(slope)*LOG(failure time)+(constant), where(slope)≧−0.0300 when the failure is ductile and where the testing isperformed according to ISO 1167:1996(E).
 10. A polypropylene compositioncomprised of a propylene random copolymer which comprises: 73.0-99.0 wt% of propylene, and 1 to 20 wt % of one or more C₄-C₈ α-olefins and/orup to 7 wt % of ethylene, where the propylene random copolymer is atleast partially crystallized in the β-modification, for the productionof pressure pipes whose failure time vs. hoop stress relation at 95° C.before a knee-point fits the following type of equation:LOG(hoop stress)=(slope)*LOG (failure time)+(constant) and where aknee-point does not occur before 1500 hrs of testing according to ISO1167:1996(E).
 11. A polypropylene according to any one of claims 9 or 10wherein the propylene random copolymer comprises: 90.0-94.0 wt % ofpropylene, and 6 to 10 wt % of 1-butene, where (slope)≧−0.0250.
 12. Apolypropylene according to any one of claims 9 or 10 wherein thepropylene random copolymer comprises: 89.4-95.9 wt % of propylene, 4 to10 wt % of 1-butene, and 0.1 to 0.6 wt % of ethylene, where(slope)≧−0.0250.
 13. A polypropylene according to any one of claims 9 or10 wherein the propylene random copolymer comprises: 97-97 wt % ofpropylene, and 3 to 5 wt % of ethylene, where (slope)≧−0.0220. 14.Multi-layer pipe where at least one of the layers is comprised of theclaims 1 2, 9 or 10.